USE BUOYS TO PREDICT EXACT SWELL ARRIVAL TIME
FOR SOUTH PACIFIC SWELLS(Applicable to Central/North California ONLY)

Southern hemisphere swells travel on average 7-8 days before reaching western US coastal waters. When a swell is within 4 days of arriving, a better prediction can be made using data from coastal buoys. The ability to determine exact arrival time is much less if the swell is roughly from 180 degrees, because it is outside the range of Buoy 51028 (Christmas Island). In such cases, the forewarning for such swells averages less than 12 hours due to the lack of buoys off Central and South America.

These tables help you to establish the swell arrival time on Northern California beaches (relative to San Francisco) providing you know roughly what the swell direction is. Estimate the swell direction based on the storms position relative to San Francisco using the tables in Appendix A. Once the swell begins to hit one of the outer buoys listed below (like 51028), write down the time and period of the first reading. Then select the appropriate table based on the estimated swell direction. Browse over to the period column, select the period of the swell that hit buoy 51028, and browse over to the travel time column that corresponds to that period reading and write that value down. For example, if a 20 second period swell hit 51028 at 10 AM on Monday from 200 degrees, then that swell should hit San Francisco 87 hours later, or on 1 AM Friday.

Swell Angle: 180 Degrees

Hit Order

Buoy Number

Distance from Pillar Point (nmiles)*

Period
(sec)

Travel Time
(Hrs) & (Days/Hrs) **

Buoy Distance from Pillar Point Travel Line ***

1

46025
Catalina Is

240

@14

11

<200 nmiles off focus

@17

9.1

@20

7.7

@25

6.2

2

46028
Cape San Martin

105

@14

4.8

<100 nmiles off focus

@17

4.0

@20

3.4

@25

2.7

Swell Angle: 200 Degrees

Hit Order

Buoy Number

Distance from Pillar Point (nmiles)*

Period
(sec)

Travel Time
(Hrs) & (Days/Hrs) **

Buoy Distance from Pillar Point Travel Line ***

1

51028
Christmas Island

2700

@14

1245/3

500 nmiles
WNW of
focus

@17

1024/4

@20

873/15

@25

693/21

2

51002
SW Hawaii

1450

@14

67.02/20

1200 nmiles WNW of focus

@17

552/8

@20

471/23

@25

371/13

3

46025
Catalina Is

140

@14

6.4

<200 nmiles off focus

@17

5.3

@20

4.5

@25

3.6

4

46028
Cape San Martin

80

@14

3.7

<100 nmiles off focus

@17

3

@20

2.6

@25

2.1

Swell Angle: 220 Degrees

Hit Order

Buoy Number

Distance from Pillar Point (nmiles)*

Period
(sec)

Travel Time
(Hrs) & (Days/Hrs) **

Buoy Distance from Pillar Point Travel Line ***

1

51028
Christmas Island

2800

@14

1285/9

200 nmiles
WNW of focus

@17

1064/11

@20

903/18

@25

723

2

51002
SW Hawaii

1800

@14

833/11

1000 nmiles NW of focus

@17

682/19

@20

582/10

@25

461/22

3

46025
Catalina Is

55

@14

2.6

<200 nmiles off focus

@17

2.1

@20

1.8

@25

1.5

4

46028
Cape San Martin

55

@14

2.5

<100 nmiles off focus

@17

2.1

@20

1.8

@25

1.5

APPENDIX AEstimated Swell Direction Based on Storm Position
(This table also provides another alternative for determining Swell Travel Time)